Oxford defines "cataract" as "a steep waterfall" as well as gives the more common meaning of the word i.e. the medical condition that causes a loss of sight.
Also, "cataract", as meaning "waterfall", is used in literature. The following is from Wordsworth's Intimation of Immortality
And I again am strong:
The cataracts blow their trumpets from the steep
This is an odd pair of meanings being of the same word. Is there is any reason why "cataract" means both "waterfall and "loss of sight"?